Conventionally, motorcycle engines (internal combustion engines) having an oil pan are known. For example, Japanese Patent Document JP-B-3411894 discloses a motorcycle engine including: an output gear that rotates together with a crankshaft; a clutch gear (speed reduction gear) meshed with the output gear to be rotated as the output gear rotates; and a pump gear meshed with the clutch gear in the vicinity of the lowermost end of the clutch gear to rotate as the clutch gear rotates.
In the above example where the motorcycle engine (internal combustion engine) has an oil pan for reserving oil, however, the pump gear may disadvantageously contact the oil and agitate the oil, because the pump gear is meshed with the clutch gear (speed reduction gear) in the vicinity of the lowermost end of the clutch gear. In this case, a part of the rotation force of the pump gear is used to agitate the oil resulting in a loss of the driving force of the motorcycle engine.